As electronic devices become smaller and are used in greater contact with human beings, the importance of electrical safety continually increases. Even relatively small electrical current levels can harm the human body. For example, current levels as low as 60 milliamps (mA) flowing from one hand to the other in a human adult can cause a heart to experience ventricular fibrillation.
Electrical safety is of significant concern in the area of medical devices. Many varieties of electronic medical devices exist that require conductive contact with at least a portion of the human body. Examples of such devices include: ambulatory pumps, pacemakers, electrical leads for delivery of defibrillation pulses or measurement of ElectroCardioGram (ECG) signals, and drug delivery devices. In some circumstances, multiple devices are in conductive contact with the same patient at the same time.
Electrical safety is perhaps of the greatest concern for those devices that are adapted to be placed in contact with intravenous fluids in the human body. This is because the human circulatory system primarily consists of water, which is highly conductive. Electrical safety is a particular concern for devices that are adapted to supply fluid to the human circulator system, because the delivered fluid creates a direct and highly conductive path for harmful currents to reach the human body.
It is often desirable that medical devices be communicatively coupled with a peripheral device such that the device can communicate with the peripheral device to program the device or communicate data and other information. One example of a peripheral device is a personal computer. Some medical devices include a data port that allows an electrical data connection to be made between the medical device and the peripheral device. A medical device may be may be adapted to communicate with a peripheral device using a passive connection or an active connection. A passive connection is one in which electrical signals are transmitted for purposes of communicating data only. In contrast, active devices are those that allow power to be transferred from the peripheral device to the medical device. Examples of passive connections include: RS-232, IEEE 488, Medical Information Bus, Ethernet connection, telephone style connectors, or any other standard or non-standard connector. Examples of active connections include Universal Serial Bus (USB), FireWire, and Power over Ethernet (PoE) connections.
Typically, the danger that exists as a result of the use of electronic devices that are in contact with a patient requires that the medical device be disconnected from contact with the patient in order to connect a peripheral device. This limits a physician or other user, because the removal of the device prevents capture of real-time data from the device while it is connected to the patient. Also, the removal of the device itself may be very cumbersome and time consuming, and may further expose the patient to risk (such as where a needle is removed).
One way in which a medical device can be designed to avoid the hazards associated with electrical medical devices is to electrically isolate the device from the peripheral device. In this context, isolation typically takes the form of translating an electrical signal to some other medium, such as an optical signal, to avoid the transfer of electrical current, and thus the hazards associated with the use of such devices as discussed above.
Some examples of optical isolators are described in the following U.S. Patent documents: US Publ. Appl. No. 2005/0001179 to Gisler et al., U.S. Pat. No. 6,617,846 to Hayat-Dawoodi et al., US Publ. Appl. No. 2004/0113498 to Kroenke, and U.S. Publ. Appl. No. 2006/0265540 to Mass et al., all of which are incorporated by reference in their entirety herein. Optical isolators work by operating one or more light emitting elements (such as a light emitting diode) to transmit light in response to the contents of an electrical signal on one side of the medical device/peripheral device interface. On the other side of the medical device/peripheral device interface, at least some of the transmitted light is collected by a light sensitive electrical device such as a photodiode. The received light is then translated into an electrical current by the light sensitive electrical device. Thus, the original electrical signal is communicated across the medical device/peripheral device interface without conduction of an electrical current. Optical isolators are advantageous in that they provide low-cost and reliable isolation of an electrical signal. However, optical isolators are limited in that they are only capable of effectively isolating an electrical signal transmitted at relatively slower data rates. Therefore, a need exists to provide improved devices and methods providing for a more reliable, higher-speed electrical isolation of signals for use in ambulatory medical devices which utilize active peripheral interface connections.